Increases in lung and brain water following experimental stroke: Effect of mannitol and hypertonic saline*

Focus on brain-lung crosstalk: Preventing or treating the pathological vicious circle between the brain and the lung

Recently, there has been increasing attention to bidirectional information exchange between the brain and lungs. Typical physiological data is communicated by channels like the circulation and sympathetic nervous system. However, communication between the brain and lungs can also occur in pathological conditions. Studies have shown that severe traumatic brain injury (TBI), cerebral hemorrhage, subarachnoid hemorrhage (SAH), and other brain diseases can lead to lung damage. Conversely, severe lung diseases such as acute respiratory distress syndrome (ARDS), pneumonia, and respiratory failure can exacerbate neuroinflammatory responses, aggravate brain damage, deteriorate neurological function, and result in poor prognosis. A brain or lung injury can have adverse effects on another organ through various pathways, including inflammation, immunity, oxidative stress, neurosecretory factors, microbiome and oxygen. Researchers have increasingly concentrated on possible links between the brain and lungs. However, there has been little attention given to how the interaction between the brain and lungs affects the development of brain or lung disorders, which can lead to clinical states that are susceptible to alterations and can directly affect treatment results. This review described the relationships between the brain and lung in both physiological and pathological conditions, detailing the various pathways of communication such as neurological, inflammatory, immunological, endocrine, and microbiological pathways. Meanwhile, this review provides a comprehensive summary of both pharmacological and non-pharmacological interventions for diseases related to the brain and lungs. It aims to support clinical endeavors in preventing and treating such ailments and serve as a reference for the development of relevant medications.

Brain to periphery in acute ischemic stroke: Mechanisms and clinical significance

The social and public health burdens of ischemic stroke have been increasing worldwide. In addition to focal brain damage, acute ischemic stroke (AIS) provokes systemic abnormalities across peripheral organs. AIS profoundly alters the autonomic nervous system, hypothalamic-pituitary-adrenal axis, and immune system, which further yield deleterious organ-specific consequences. Poststroke systemic pathological alterations in turn considerably contribute to the progression of ischemic brain injury, which accounts for the substantial impact of systemic complications on stroke outcomes. This review provides a comprehensive and updated pathophysiological model elucidating the systemic effects of AIS. To address their clinical significance and inform stroke management, we also outline the resulting systemic complications at particular stages of AIS and highlight the mechanisms. Future therapeutic strategies should attempt to integrate the treatment of primary brain lesions with interventions for secondary systemic complications, and should be tailored to patient individualized characteristics to optimize stroke outcomes.

Lung-Derived SOD3 Attenuates Neurovascular Injury After Transient Global Cerebral Ischemia

Background

Systemic innate immune priming is a recognized sequela of post‐ischemic neuroinflammation and contributor to delayed neurodegeneration. Given mounting evidence linking acute stroke with reactive lung inflammation, we asked whether enhanced expression of the endogenous antioxidant extracellular superoxide dismutase 3 (SOD3) produced by alveolar type II pneumocytes would protect the lung from transient global cerebral ischemia and the brain from the delayed effects of ischemia‐reperfusion.

Methods and Results

Following 15 minutes of global cerebral ischemia or sham conditions, transgenic SOD3 and wild‐type mice were followed daily for changes in weight, core temperature, and neurological function. Three days after reperfusion, arterial and venous samples were collected for complete blood counts, flow cytometry, and SOD3 protein blotting, and immunohistochemistry was performed on lung and brain tissue to assess tissue injury, blood‐brain barrier permeability, and neutrophil transmigration. Relative to ischemic controls, transgenic SOD3 mice performed better on functional testing and exhibited reduced peripheral neutrophil activation, lung inflammation, and blood‐brain barrier leak. Once released from the lung, SOD3 was predominantly not cell associated and depleted in the venous phase of circulation.

Conclusions

In addition to reducing the local inflammatory response to cerebral ischemia, targeted enrichment of SOD3 within the lung confers distal neuroprotection against ischemia‐reperfusion injury. These data suggest that therapies geared toward enhancing adaptive lung‐neurovascular coupling may improve outcomes following acute stroke and cardiac arrest.

Lung injury in brain ischemia/reperfusion is exacerbated by mechanical ventilation with moderate tidal volume in rats

Ischemic stroke is one of the most frequent causes of injury in the central nervous system which may lead to multiorgan dysfunction, including in the lung. The aim of this study was to investigate whether brain ischemia/reperfusion with or without mechanical ventilation leads to lung injury. Male Sprague-Dawley rats were assigned to four groups: Sham, 1-h brain ischemia (MCAO)/24-h reperfusion (I/R), mechanical ventilation with moderate tidal volume (MTV), and I/R+MTV. The pulmonary capillary permeability (K_fc) was measured in the isolated perfused lung. Mean arterial blood pressure (MAP), heart rate (HR), blood-gas variables, histopathological parameters, lung glutathione peroxidase, and TNF-α were measured. K_fc in the I/R, MTV, and I/R+MTV groups were higher than that in the Sham group. In the I/R, MTV, and I/R+MTV groups, arterial partial pressures of oxygen and the arterial partial pressure of oxygen/fraction of inspired oxygen ratios were lower, whereas arterial partial pressures of carbon dioxide were higher than those in the Sham group. The histopathological score in the I/R group was more than that in the Sham group, and in the MTV and I/R+MTV groups were higher than those in the Sham and I/R groups. Furthermore, there were stepwise rises in TNF-α in the I/R, MTV, and I/R+MTV groups, respectively. There was no significant difference in MAP between groups. However, HR in the MTV group was higher than that in the Sham group. Brain ischemia/reperfusion leads to pulmonary capillary endothelial damage and the impairment of gas exchange in the alveolar-capillary barrier, which is exacerbated by mechanical ventilation with moderate tidal volume partially linked to inflammatory reactions.

Hypertonic saline reduces cell infiltration into the lungs after brain death in rats

BACKGROUND

Lung transplantation is a treatment method for end stage lung disease, but the availability of donor lungs remains a major constraint. Brain death (BD) induces hemodynamic instability with microcirculatory hypoperfusion and increased inflammation, leading to pulmonary dysfunction. Hypertonic saline solution (HSS) is a volume expander possessing immunomodulatory effects. This study evaluated the influence of HSS on pulmonary dysfunction and inflammation in a rat model of BD.

METHODS

BD was induced by inflation of an intracranial balloon catheter. Rats were divided into [1]: Sham, without BD [2]; NS, NaCl treatment (0.9%, 4 mL/kg, i.v.) immediately after BD [3]; HSS₁, HSS treatment (NaCl 7.5%, 4 mL/kg, i.v.) immediately after BD; and [4] HSS₆₀, HSS treatment 60 min post BD. All groups were analyzed after 360 min.

RESULTS

Animals subjected to BD exhibited increased exhaled O₂ and decreased CO₂.The number of leukocytes in the lungs was significantly increased in the NS group (p = 0.002) and the HSS treatment was able to reduce it (HSS₁, p = 0.018 and HSS₆₀ = 0.030). In parallel, HSS-treated rats showed reduced levels of ICAM-1 expression, which was increased in the NS compared to Sham group. Lung edema was found increased in the NS group animals compared to Sham and no effect of the HSS treatment was observed. There were no differences among the groups in terms of TNF-α, VEGF, and CINC-1 lung concentrations.

CONCLUSIONS

HSS is capable of reducing inflammatory cell infiltration into the lung after BD induction, which is associated with the reduction of ICAM-1 expression in organ vessels.

The post-cardiac arrest syndrome: A case for lung-brain coupling and opportunities for neuroprotection

Systemic inflammation and multi-organ failure represent hallmarks of the post-cardiac arrest syndrome (PCAS) and predict severe neurological injury and often fatal outcomes. Current interventions for cardiac arrest focus on the reversal of precipitating cardiac pathologies and the implementation of supportive measures with the goal of limiting damage to at-risk tissue. Despite the widespread use of targeted temperature management, there remain no proven approaches to manage reperfusion injury in the period following the return of spontaneous circulation. Recent evidence has implicated the lung as a moderator of systemic inflammation following remote somatic injury in part through effects on innate immune priming. In this review, we explore concepts related to lung-dependent innate immune priming and its potential role in PCAS. Specifically, we propose and investigate the conceptual model of lung-brain coupling drawing from the broader literature connecting tissue damage and acute lung injury with cerebral reperfusion injury. Subsequently, we consider the role that interventions designed to short-circuit lung-dependent immune priming might play in improving patient outcomes following cardiac arrest and possibly other acute neurological injuries.

Focal ischemic stroke leads to lung injury and reduces alveolar macrophage phagocytic capability in rats

BACKGROUND

Ischemic stroke causes brain inflammation, which we postulate may result in lung damage. Several studies have focused on stroke-induced immunosuppression and lung infection; however, the possibility that strokes may trigger lung inflammation has been overlooked. We hypothesized that even focal ischemic stroke might induce acute systemic and pulmonary inflammation, thus altering respiratory parameters, lung tissue integrity, and alveolar macrophage behavior.

METHODS

Forty-eight Wistar rats were randomly assigned to ischemic stroke (Stroke) or sham surgery (Sham). Lung function, histology, and inflammation in the lung, brain, bronchoalveolar lavage fluid (BALF), and circulating plasma were evaluated at 24 h. In vitro, alveolar macrophages from naïve rats (unstimulated) were exposed to serum or BALF from Sham or Stroke animals to elucidate possible mechanisms underlying alterations in alveolar macrophage phagocytic capability. Alveolar macrophages and epithelial and endothelial cells of Sham and Stroke animals were also isolated for evaluation of mRNA expression of interleukin (IL)-6 and tumor necrosis factor (TNF)-α.

RESULTS

Twenty-four hours following ischemic stroke, the tidal volume, expiratory time, and mean inspiratory flow were increased. Compared to Sham animals, the respiratory rate and duty cycle during spontaneous breathing were reduced, but this did not affect lung mechanics during mechanical ventilation. Lungs from Stroke animals showed clear evidence of increased diffuse alveolar damage, pulmonary edema, and inflammation markers. This was associated with an increase in ultrastructural damage, as evidenced by injury to type 2 pneumocytes and endothelial cells, cellular infiltration, and enlarged basement membrane thickness. Protein levels of proinflammatory mediators were documented in the lung, brain, and plasma (TNF-α and IL-6) and in BALF (TNF-α). The phagocytic ability of macrophages was significantly reduced. Unstimulated macrophages isolated from naïve rats only upregulated expression of TNF-α and IL-6 following exposure to serum from Stroke rats. Exposure to BALF from Stroke or Sham animals did not change alveolar macrophage behavior, or gene expression of TNF-α and IL-6. IL-6 expression was increased in macrophages and endothelial cells from Stroke animals.

CONCLUSIONS

In rats, focal ischemic stroke is associated with brain-lung crosstalk, leading to increased pulmonary damage and inflammation, as well as reduced alveolar macrophage phagocytic capability, which seems to be promoted by systemic inflammation.

Brain-Derived Glia Maturation Factor β Participates in Lung Injury Induced by Acute Cerebral Ischemia by Increasing ROS in Endothelial Cells

Brain damage can cause lung injury. To explore the mechanism underlying the lung injury induced by acute cerebral ischemia (ACI), we established a middle cerebral artery occlusion (MCAO) model in male Sprague-Dawley rats. We focused on glia maturation factor β (GMFB) based on quantitative analysis of the global rat serum proteome. Polymerase chain reaction, western blotting, and immunofluorescence revealed that GMFB was over-expressed in astrocytes in the brains of rats subjected to MCAO. We cultured rat primary astrocytes and confirmed that GMFB was also up-regulated in primary astrocytes after oxygen-glucose deprivation (OGD). We subjected the primary astrocytes to Gmfb RNA interference before OGD and collected the conditioned medium (CM) after OGD. We then used the CM to culture pulmonary microvascular endothelial cells (PMVECs) acquired in advance and assessed their status. The viability of the PMVECs improved significantly when Gmfb was blocked. Moreover, ELISA assays revealed an elevation in GMFB concentration in the medium after OGD. Cell cultures containing recombinant GMFB showed increased levels of reactive oxygen species and a deterioration in the state of the cells. In conclusion, GMFB is up-regulated in astrocytes after ACI, and brain-derived GMFB damages PMVECs by increasing reactive oxygen species. GMFB might thus be an initiator of the lung injury induced by ACI.

The Effects of Clinically Relevant Hypertonic Saline and Conivaptan Administration on Ischemic Stroke

Cerebral edema after stroke is associated with poor neurological outcomes. Current therapies are limited to osmotic agents, such as hypertonic saline (HS), which reduce intracranial pressure. Although studies have demonstrated edema reductions following HS, tissue survival has not been thoroughly examined. Additionally, the efficacy of promising pharmacological agents has not been evaluated for synergy with osmotic agents. Conivaptan is an FDA-approved vasopressin receptor antagonist that may exert both osmotic and anti-inflammatory effects. In this study, rats were subjected to middle cerebral artery occlusion prior to treatment with 5 % HS bolus +5 % HS maintenance (HS), conivaptan alone (Con), conivaptan +5 % HS maintenance (Con + HS), or conivaptan +5 % HS bolus +5 % maintenance (Con + HSb). Treatments were initiated at six (Early) or 24 h (Late) following stroke and rats were euthanized at 48 h to evaluate infarct volume, brain edema, and microglia/macrophage activation. Infarct volume and brain edema in the Early HS, Early Con, and Late HS groups were significantly reduced compared with controls. Interestingly, only the Early Con group demonstrated reduced microglia/macrophage activation. These data suggest an anti-inflammatory mechanism for conivaptan and provide support for a multipronged approach combining osmotic agents with compounds that inhibit the neuroinflammatory response to stroke.

Cross-talk between the inflammatory response, sympathetic activation and pulmonary infection in the ischemic stroke

The immune system response and inflammation play a key role in brain injury during and after a stroke. The acute immune response is responsible for secondary brain tissue damage immediately after the stroke, followed by immunosuppression due to sympathetic nervous system activation. The latter increases risk of infection complications, such as pneumonia. The pneumonia-related inflammatory state can release a bystander autoimmune response against central nervous system antigens, thereby initiating a vicious circle. The aim of this review is to summarize the relationship between ischemic stroke, sympathetic nervous system activation and pulmonary infection.

Methods to assess tissue permeability

An essential requirement for adequate organ performance is the formation of permeability barriers that separate and maintain compartments of distinctive structure and function. The endothelial cell lining of the vasculature defines a semipermeable barrier between the blood and interstitial spaces of all organs. Disruption of the endothelial cell barrier can result in increased permeability and vascular leak. These effects are associated with multiple systemic disease processes and can accompany acute tissue responses to injury. The mechanisms that control barrier function are complex and their full understanding requires a multidisciplinary approach. The use of in vivo permeability data often complements molecular findings and adds power to the studies. The interaction of multiple cell types and tissues present only in mammalian models allows for testing of hypothesis and establishing the physiological significance of the results. In this chapter we describe simple methods that can be used systematically to measure the permeability profile of several organs.

Real time estimation of brain water content in comatose patients

OBJECTIVE

Although brain swelling is an important cause of neurological deterioration, real time measurement of brain edema does not currently exist. Because thermal conductivity is proportional to percentage water content, we used the thermal conductivity constant to estimate brain water content (BWC).

METHODS

Between June 2008 and November 2010, 36 comatose brain-injured patients underwent cerebral blood flow monitoring using a thermal diffusion probe in our neurocritical care unit. BWC was estimated hourly utilizing the measured thermal conductivity and the known temperature-adjusted thermal conductivity of water. In vitro experiments were performed to validate this formula using agar, glycerol, and water mixtures with different water content.

RESULTS

Thermal conductivity was highly correlated (R(2) = 0.99) and estimated water content was well correlated with actual water content (mean difference, 0.58%) in the in vitro preparations. The majority of the 36 patients (median age, 57 years; 44% female) had subarachnoid hemorrhage (n = 14) or cardiac arrest (n = 9). Initial BWC at the time of monitoring ranged from 67.3 to 85.5%. Brain regions appearing edematous on computed tomography showed higher estimated BWC than normal-appearing brain regions (79.1 vs 70.2%; p < 0.01). Bolus osmotherapy (20% mannitol or 23.4% hypertonic saline) decreased BWC from 77.2 ± 0.7% (mean ± standard error) at baseline to 76.1 ± 0.5% at 1 hour, 76.5 ± 0.3% at 2 hours, and 76.7 ± 0.2% at 3 hours (all p ≤ 0.03).

INTERPRETATION

Real time monitoring of BWC is feasible using thermal conductivity. Further studies are needed to confirm the clinical utility of this technique.

Cerebral hemodynamic and metabolic effects of equi-osmolar doses mannitol and 23.4% saline in patients with edema following large ischemic stroke

INTRODUCTION

Cerebral edema after ischemic stroke is frequently treated with mannitol and hypertonic saline (HS); however, their relative cerebrovascular and metabolic effects are incompletely understood, and may operate independent of their ability to lower intracranial pressure.

METHODS

We compared the effects of 20% mannitol and 23.4% saline on cerebral blood flow (CBF), blood volume (CBV), oxygen extraction fraction (OEF), and oxygen metabolism (CMRO(2)), in nine ischemic stroke patients who deteriorated and had >2 mm midline shift on imaging. (15)O-PET was performed before and 1 h after administration of randomly assigned equi-osmolar doses of mannitol (1.0 g/kg) or 23.4% saline (0.686 mL/kg).

RESULTS

Baseline CBF values (ml/100g/min) in the infarct core, periinfarct region, remaining ipsilateral hemisphere, and contralateral hemisphere in the mannitol group were 5.0 ± 3.9, 25.6 ± 4.4, 35.6 ± 8.6, and 45.5 ± 2.2, respectively, and in the HS group were 8.3 ± 9.8, 35.3 ± 10.9, 38.2 ± 15.1, and 35.2 ± 12.4, respectively. There was a trend for CBF to rise in the contralateral hemisphere after mannitol from 45.5 ± 12.2 to 57.6 ± 21.7, P = 0.098, but not HS. CBV, OEF, and CMRO(2) did not change after administration of either agent. Change in CBF in the contralateral hemisphere after osmotic therapy was strongly correlated with baseline blood pressure (R (2)= 0.879, P = 0.002).

CONCLUSIONS

We conclude that at higher perfusion pressures, osmotic agents may raise CBF in non-ischemic tissue. We conclude that at higher perfusion pressures, osmotic agents may raise CBF in non-ischemic tissue.

Hypertonic saline in patients with poor-grade subarachnoid hemorrhage improves cerebral blood flow, brain tissue oxygen, and pH

BACKGROUND AND PURPOSE

Delayed cerebral ischemia and infarction due to reduced CBF remains the leading cause of poor outcome after aneurysmal subarachnoid hemorrhage. Hypertonic saline (HS) is associated with an increase in CBF. This study explores whether CBF enhancement with HS in patients with poor-grade subarachnoid hemorrhage is associated with improved cerebral tissue oxygenation.

METHODS

Continuous monitoring of arterial blood pressure, intracranial pressure, cerebral perfusion pressure, brain tissue oxygen, carbon dioxide, pH, and middle cerebral artery flow velocity was performed in 44 patients. Patients were given an infusion (2 mL/kg) of 23.5% HS. In 16 patients, xenon CT scanning was also performed. CBF in a region surrounding the tissue oxygen sensor was calculated. Data are mean+/-SD.

RESULTS

Thirty minutes postinfusion, a significant increase in arterial blood pressure, cerebral perfusion pressure, flow velocity, brain tissue pH, and brain tissue oxygen was seen together with a decrease in intracranial pressure (P<0.05). Intracranial pressure remained reduced for >300 minutes and flow velocity elevated for >240 minutes. A significant increase in brain tissue oxygen persisted for 240 minutes. Average baseline regional CBF was 33.9+/-13.5 mL/100 g/min, rising by 20.3%+/-37.4% (P<0.05) after HS. Patients with favorable outcome responded better to HS in terms of increased CBF, brain tissue oxygen, and pH and reduced intracranial pressure compared with those with an unfavorable outcome. A sustained increase in brain tissue oxygen (beyond 210 minutes) was associated with favorable outcome (P<0.023).

CONCLUSIONS

HS augments CBF in patients with poor-grade subarachnoid hemorrhage and significantly improves cerebral oxygenation for 4 hours postinfusion. Favorable outcome is associated with an improvement in brain tissue oxygen beyond 210 minutes.

Isotonic and hypertonic crystalloid solutions in the critically ill

Disorders of fluid and electrolyte balance in the critically ill are volume-related, compositional, or both. Targeting 'normal' values for plasma volume, osmolality and electrolytes might not be optimal in conditions as diverse as intracranial trauma/haemorrhage, hepatic encephalopathy, abdominal hypertension, or major surgery, because a hyperosmolar state seems to favourably affect tissue (brain and intestinal) oedema formation. However, adequately powered studies regarding the impact of hypertonic saline on outcome are lacking. Isotonic crystalloids are the cornerstone of resuscitation and must be balanced against natural or artificial colloids and vasopressors. Crystalloid resuscitation is superior to vasopressors in shock associated with blunt trauma, and is at least not inferior to colloids in septic shock. Traditional rules of thumb indicating the need for three to four times the amount of crystalloids for the plasma volume to be replaced are probably erroneous and might have contributed to association of overly aggressive crystalloid resuscitation with poor outcome.

Management of acute ischemic stroke

Stroke is the third leading cause of death and the leading cause of disability in the United States. This article summarizes the management of acute ischemic stroke, including conventional and novel therapies. The article provides an overview of the initial management, diagnostic work-up, treatment options, and supportive measures that need to be considered in the acute phase of ischemic stroke.

Enhancement of cerebral blood flow using systemic hypertonic saline therapy improves outcome in patients with poor-grade spontaneous subarachnoid hemorrhage

OBJECT

Systemic administration of 23.5% hypertonic saline enhances cerebral blood flow (CBF) in patients with poor-grade spontaneous subarachnoid hemorrhage (SAH). Whether the increment of change in CBF correlates with changes in autoregulation of CBF or outcome at discharge remains unknown.

METHODS

Thirty-five patients with poor-grade spontaneous SAH received 2 ml/kg 23.5% hypertonic saline intravenously, and they underwent bedside transcranial Doppler (TCD) ultrasonography and intracranial pressure (ICP) monitoring. Seventeen of them underwent Xe-enhanced computed tomography (CT) scanning for measuring CBF. Outcome was assessed using the modified Rankin Scale (mRS) at discharge from the hospital. The data were analyzed using repeated-measurement analysis of variance and Dunnett correction. A comparison was made between patients with favorable and unfavorable outcomes using multivariate logistic regression.

RESULTS

The authors observed a maximum increase in blood pressure by 10.3% (p < 0.05) and cerebral perfusion pressure (CPP) by 21.2% (p < 0.01) at 30 minutes, followed by a maximum decrease in ICP by 93.1% (p < 0.01) at 60 minutes. Changes in ICP and CPP persisted for longer than 180 and 90 minutes, respectively. The results of TCD ultrasonography showed that the baseline autoregulation was impaired on the ipsilateral side of ruptured aneurysm, and increments in flow velocities were higher and lasted longer on the contralateral side (48.75% compared with 31.96% [p = 0.045] and 180 minutes compared with 90 minutes [p < 0.05], respectively). The autoregulation was briefly impaired on the contralateral side during the infusion. A dose-dependent effect of CBF increments on favorable outcome was seen on Xe-CT scans (mRS Score 1-3, odds ratio 1.27 per 1 ml/100 g tissue x min, p = 0.045).

CONCLUSIONS

Bolus systemic hypertonic saline therapy may be used for reversal of cerebral ischemia to normal perfusion in patients with poor-grade SAH.

Activity of mannitol and hypertonic saline therapy on the oxidant and antioxidant system during the acute term after traumatic brain injury in the rats

In this study, our objective is to investigate the effects of mannitol and 7.5% hypertonic saline (HS) therapy on the levels of malondialdehyde (MDA), catalase and glutathione peroxidase (GSH-Px) in the early stages of experimental head traumas in rats. Rats included in the study were divided into four groups: Group I Control, Group II Trauma, Group III Mannitol, and Group IV 7.5% Hypertonic Saline. Rats in Group II were subject to head trauma only. Mannitol was injected intraperitoneally to rats in Group III after head trauma and 7.5% HS was injected intraperitoneally to rats in Group IV after head trauma. Rats were sacrificed 4 h after administration of mannitol or 7.5% HS, and the levels of MDA catalase and GSH-Px in brain tissues extracted from rats were determined. MDA levels in the trauma group were significantly increased compared with the control group (p<0.01), whereas there was a reduction in catalase and GSH-Px levels, although these differences were not significant. By contrast, in the mannitol group, MDA, catalase and GSH-Px levels were lower than the levels in the trauma group, and these reductions were statistically significant (p<0.05). The MDA, catalase and GSH-Px levels of the 7.5% HS group were lower than those of the trauma group; however, this reduction was not statistically significant. It was concluded that mannitol and 7.5% HS therapies that are used to reduce intracranial pressure and to increase the use of catalase, an antioxidant enzyme, and GSH-Px, are likely to reduce cellular damage by reducing the formation of MDA, the levels of which are known to be indicative of cellular level oxidant damage.

Hypertonic saline: first-line therapy for cerebral edema?

This article highlights the experimental and clinical data, controversies and postulated mechanisms surrounding osmotherapy with hypertonic saline (HS) solutions in the neurocritical care arena and builds on previous reviews on the subject. Special attention is focused on HS therapy on commonly encountered clinical paradigms of acute brain injury including traumatic brain injury (TBI), post-operative "retraction edema", intracranial hemorrhage (ICH), tumor-associated cerebral edema, and ischemia associated with ischemic stroke.

Medical management of cerebral edema

✓Cerebral edema is frequently encountered in clinical practice in critically ill patients with acute brain injury from diverse origins and is a major cause of increased morbidity and death in this subset of patients. The consequences of cerebral edema can be lethal and include cerebral ischemia from compromised regional or global cerebral blood flow (CBF) and intracranial compartmental shifts due to intracranial pressure gradients that result in compression of vital brain structures. The overall goal of medical management of cerebral edema is to maintain regional and global CBF to meet the metabolic requirements of the brain and prevent secondary neuronal injury from cerebral ischemia. Medical management of cerebral edema involves using a systematic and algorithmic approach, from general measures (optimal head and neck positioning for facilitating intracranial venous outflow, avoidance of dehydration and systemic hypotension, and maintenance of normothermia) to specific therapeutic interventions (controlled hyperventilation, administration of corticosteroids and diuretics, osmotherapy, and pharmacological cerebral metabolic suppression). This article reviews and highlights the medical management of cerebral edema based on pathophysiological principles in acute brain injury.

Effect of osmotherapy with hypertonic saline on regional cerebral edema following experimental stroke: a study utilizing magnetic resonance imaging

INTRODUCTION

Hypertonic saline (HS) solutions are increasingly being utilized as osmotherapeutic agents for the treatment of cerebral edema associated with brain injury from diverse etiologies.

METHODS

In a rat model of permanent focal ischemia, we (1) determined the effect of HS therapy on regional brain water content with T(1)- and T(2)-weighted magnetic resonance imaging (MRI) and (2) tested the hypothesis that HS therapy modulates the expression of aquaporin-4 (AQP4) in the ischemic brain.

RESULTS

Halothane-anesthetized male Wistar rats were subjected to permanent middle cerebral artery occlusion (MCAO) and at 6 hr post-MCAO were treated with either continuous intravenous infusion of 0.9% saline (NS) or 7.5% HS for 18 hr. While lesion size measured on T(2)-weighted imaging did not differ between NS (580 +/- 217 mm(3); mean +/- SD) and HS (460 +/- 86 mm(3)) treatments, there was a correlation between T(2) values and tissue water content as determined by wet-to-dry ratio in the caudoputamen (CP) complex of ischemic core (r = 0.612, P < 0.05). There were significant differences in T(1) values with treatment in the ischemic cortex (NS: 2.08 +/- 0.13; HS: 1.78 +/- 0.20) and CP complex (NS: 2.09 +/- 0.14; HS: 1.77 +/- 0.22), but there was no correlation between T(2) values and regional brain tissue water content in the peri-infarct regions and the non-ischemic hemisphere. There were significant differences in AQP4 protein expression in the ischemic hemisphere between NS and HS-treated rats.

CONCLUSIONS

These data demonstrate that (1) T(2)-weighted MRI imaging correlates with tissue water content in the ischemic core but not in the peri-infarct regions, and (2) attenuation of ischemia-evoked cerebral edema involves the modulation of AQP4 channels in the brain.

Critical care of acute ischemic stroke

Stroke is the third leading cause of death and the leading cause of disability in the United States. This article summarizes the critical care of acute ischemic stroke, including conventional and novel therapies. The article provided an overview of the initial management, diagnostic workup, treatment options, and supportive measures that need to be considered in the acute phase of ischemic stroke.

Neurogenic pulmonary edema

Neurogenic pulmonary edema (NPE) is usually defined as an acute pulmonary edema occurring shortly after a central neurologic insult. It has been reported regularly for a long time in numerous and various injuries of the central nervous system in both adults and children, but remains poorly understood because of the complexity of its pathophysiologic mechanisms involving hemodynamic and inflammatory aspects. NPE seems to be under-diagnosed in acute neurologic injuries, partly because the prevention and detection of non-neurologic complications of acute cerebral insults are not at the forefront of the strategy of physicians. The presence of NPE should be high on the list of diagnoses when patients with central neurologic injury suddenly become dyspneic or present with a decreased P(a)o(2)/F(i)o(2) ratio. The associated mortality rate is high, but recovery is usually rapid with early and appropriate management. The treatment of NPE should aim to meet the oxygenation needs without impairing cerebral hemodynamics, to avoid pulmonary worsening and to treat possible associated myocardial dysfunction. During brain death, NPE may worsen myocardial dysfunction, preventing heart harvesting.

The effect of mannitol on oxygenation and creatine kinase MB release in patients undergoing multivessel off-pump coronary artery bypass surgery

OBJECTIVES

Despite avoiding cardiopulmonary bypass, off-pump coronary artery bypass surgery is associated with reduction in PaO2 and postoperative respiratory compliance. Also, transient interruption of coronary flow is necessary during distal anastomoses and may impose ischemia-reperfusion myocardial injury. Mannitol is an osmotic diuretic with free radical scavenging properties, and we have evaluated the effects of mannitol on oxygenation and cardiac enzyme release in patients undergoing multivessel off-pump bypass surgery in a prospective, randomized, controlled, double-blind trial.

METHODS

Fifty patients were randomly allocated to receive either 20% mannitol 0.5 g/kg (n = 25) or normal saline 2.5 mL/kg (n = 25) during Y-graft construction. Pulmonary variables and serum sodium concentrations were measured 15 minutes after induction of anesthesia and sternum closure. Creatine kinase MB was measured before and after the operation. Intraoperative and postoperative fluid input and output, time to extubation, and intraoperative hemodynamic variables were also recorded.

RESULTS

PaO2 after sternum closure was significantly higher in the mannitol group, with faster time to extubation and shorter length of stay in the intensive care unit. Intraoperative urine output was significantly greater in the mannitol group, without significant differences in fluid input, serum sodium concentration, and hemodynamic variables. Number of patients with a creatine kinase MB level more than 3 times the upper limit of normal was significantly higher in the control group.

CONCLUSION

Mannitol could be safely used without adverse side effects in patients undergoing multivessel off-pump bypass surgery with beneficial effects in terms of preserving oxygenation, earlier extubation, and fewer patients with significant creatine kinase MB elevation.

Osmotherapy with hypertonic saline attenuates water content in brain and extracerebral organs

OBJECTIVE

Because of their beneficial effects in patients with hemorrhagic shock and multiple-system trauma, hypertonic saline solutions are increasingly being used perioperatively for volume resuscitation. Although the anti-edema effects of hypertonic saline on brain are well documented in a variety of brain injury paradigms, its effects on the water content on other organs has not been studied rigorously. In this study, we tested the hypothesis that a) hypertonic saline when given as an intravenous bolus and continuous infusion attenuates water content of small bowel, lung, and brain in rats without neuro-injury; and b) attenuation of stroke-associated increases in lung water is dependent on achieving a target serum osmolality.

DESIGN

Prospective laboratory animal study.

SETTING

Research laboratory in a teaching hospital.

SUBJECTS

Adult male Wistar rats.

INTERVENTIONS

In the first series of experiments, under controlled conditions of normoxia, normocarbia, and normothermia, spontaneously breathing, halothane-anesthetized (1.0-1.5%) adult male Wistar rats (280-320 g) were treated in a blinded randomized fashion with 7.5% hypertonic saline or 0.9% normal saline in a 8-mL/kg intravenous infusion for 3 hrs followed by a continuous intravenous infusion (1 mL/kg/hr) of 5% hypertonic saline or normal saline, respectively (n=10 each), for 48 hrs. A second group of rats were treated with continuous infusion only for 48 hrs of either 7.5% hypertonic saline or normal saline (1 mL/kg/hr) (n=10 each) without an intravenous bolus. Naïve rats served as controls (n=10). Tissue water content of small bowel, lung, and brain was determined by comparing the wet-to-dry ratios at the end of the experiment. In a second series of experiments, rats (n=94) were subjected to 2 hrs of transient middle cerebral artery occlusion by the intraluminal occlusion technique. At 6 hrs following middle cerebral artery occlusion, rats were treated in a blinded randomized fashion with a continuous intravenous infusion of normal saline, 3% hypertonic saline, or 7.5% hypertonic saline for 24, 48, 72, and 96 hrs. Surgical shams served as controls (n=7). Hypertonic saline was instituted as chloride/acetate mixture (50:50) in all experiments. Serum osmolality was determined at the end of the experiment in all animals.

MEASUREMENTS AND MAIN RESULTS

In rats without neuro-injury that received intravenous bolus followed by a continuous infusion, lung water content was significantly reduced with hypertonic saline (73.9+/-1.1%; 359+/-10 mOsm/L) (mean+/-sd) compared with normal saline treatment (76.1+/-0.53%; 298+/-4 mOsm/L) as was water content of small bowel (hypertonic saline, 69.1+/-5.8%; normal saline, 74.7+/-0.71%) and brain (hypertonic saline, 78.1+/-0.87%; normal saline, 79.2+/-0.38%) at 48 hrs. Stroke-associated increases in lung water content were attenuated with 7.5% hypertonic saline at all time points. There was a strong correlation between serum osmolality and attenuation of stroke-associated increases in lung water content (r=-.647)

CONCLUSIONS

Bowel, lung, and brain water content is attenuated with hypertonic saline when serum osmolality is >350 mOsm/L without adverse effect on mortality in animals with and without neuro-injury. Attenuation of water content of extracerebral organs with hypertonic saline treatment may have therapeutic implications in perioperative fluid management in patients with and without brain injury.

Effects of Crystalloid-Colloid Solutions on Traumatic Brain Injury

The purpose of this study was to compare the effects of crystalloid and crystalloid-colloid solutions administered at different times after isolated traumatic brain injury. Male Sprague-Dawley rats were randomized to receive one of three intravenous treatments (4 mL/kg body weight) at 10 min or 6 h after moderate traumatic brain injury. Treatments included hypertonic saline, hypertonic albumin, and normal albumin. Moderate injuries were produced using the controlled cortical impact injury model set at 2.0 mm, 4.0 m/sec, and 130 msec. Tissue damage and cerebral edema were measured to evaluate the effect of treatments for traumatic brain injury. Blood brain barrier permeability was assessed at different time points after injury to identify a mechanism for treatment effectiveness. Injury volume was the smallest for animals treated with hypertonic albumin at 6 h after injury compared to all other treatments and administration times. Ipsilateral brain water content was significantly attenuated with immediate normal saline-albumin treatment. The presence of colloid in the infusion solutions was associated with an improvement in tissue damage and edema following isolated head injury while hypertonic saline alone, when given immediately after injury, worsened tissue damage and edema. When hypertonic saline was administered at 6 h after injury, tissue damage and edema were not worsened. In conclusion, the presence of colloid in solutions used to treat traumatic brain injury and the timing of treatment have a significant impact on tissue damage and edema.

Hypertonic saline attenuates colonic tumor cell metastatic potential by activating transmembrane sodium conductance

Hypertonic saline (HTS) suppresses tumor cell-endothelial interactions by reducing integrin expression. This translates into reduced adhesion, migration and metastatic potential. This study determined the relative contributions of hyperosmolarity and sodium-specific hypertonicity on the inhibitory effects of HTS, the intracellular pH and sodium responses to HTS and the role of cytoskeletal remodeling in these changes. Human colonic tumor cells (LS174T) were exposed to lipopolysaccharide under isotonic, hypertonic, sodium-free (N-methyl-D-glucamine), hyperosmolar (mannitol or urea), disrupted cytoskeletal (10 microg/ml cytochalasin D) conditions or in the presence of 5-(N-ethyl-N-isopropyl)amiloride (EIPA). Beta(1) integrin expression was measured flow-cytometrically. Intracellular sodium and pH were measured with confocal laser microscopic imaging. Statistical analysis was performed with analysis of variance, and P < 0.05 was considered significant. Data are represented as mean +/- SEM. Hypertonic exposure attenuated integrin expression (62.03 +/- 4.7% of control, P < 0.04). No discernible effect was observed with sodium-free or hyperosmolar solutions. HTS evoked a cellular alkalinization (by a mean 0.2 pH units) and an increase in cytosolic sodium concentration (by a mean 12.4 mM, P < 0.001) via upregulation of sodium-hydrogen exchange. Disassembly of actin microfilaments by cytochalasin D and antiporter inhibition with EIPA abrogated the effect of hypertonicity on integrin expression and intracellular sodium and pH (P < 0.05). HTS downregulates adhesion molecule expression via a hypertonic, sodium-specific, cytoskeletally mediated mechanism that involves activation of sodium-hydrogen exchange with associated changes in intracellular pH and sodium concentrations.

Effect of duration of osmotherapy on blood-brain barrier disruption and regional cerebral edema after experimental stroke

Osmotherapy is the cornerstone of medical management for cerebral edema associated with large ischemic strokes. We determined the effect of duration of graded increases in serum osmolality with mannitol and hypertonic saline (HS) on blood-brain barrier (BBB) disruption and regional cerebral edema in a well-characterized rat model of large ischemic stroke. Halothane-anesthetized adult male Wistar rats were subjected to transient (2-h) middle cerebral artery occlusion (MCAO) by the intraluminal occlusion technique. Beginning at 6 h after MCAO, rats were treated with either no intravenous fluids or a continuous intravenous infusion (0.3 mL/h) of 0.9% saline, 20% mannitol, 3% HS, or 7.5% HS for 24, 48, 72, and 96 h. In the first series of experiments, BBB permeability was quantified by the Evans blue (EB) extravasation method. In the second series of experiments, water content was assessed by comparing wet-to-dry weight ratios in six predetermined brain regions. Blood-brain barrier disruption was maximal in rats treated with 0.9% saline for 48 h, but did not correlate with increases in serum osmolality or treatment duration with osmotic agents. Treatment with 7.5% HS attenuated water content in the periinfarct regions and all subregions of the contralateral nonischemic hemisphere to a greater extent than mannitol did with no adverse effect on survival rates. These data show that (1) BBB integrity is not affected by the duration and degree of serum osmolality with osmotic agents, and (2) attenuation of increases in brain water content with HS to target levels >350 mOsm/L may have therapeutic implications in the treatment of cerebral edema associated with ischemic stroke.

Efficacy and safety of hypertonic saline solutions in the treatment of severe head injury

BACKGROUND

The present study was undertaken to evaluate the efficacy and safety of hypertonic saline (HS) in the treatment of intracranial hypertension after severe head injury.

METHODS

This prospective, observational study was performed in an 11-bed neurosurgery intensive care unit of a teaching hospital. From February 2002 to September 2004, 18 severely head-injured patients with elevated intracranial pressure (ICP) and Glasgow Coma Scale scores of 5 to 8 (mean, 5.9 +/- 1.2) were admitted to the unit and treated according to a standard protocol. One dose per day of 3% saline was administered by rapid infusion (300 mL/20 min) when ICP values exceeded 20 mm Hg. After infusion, cerebral blood flow, ICP, blood pressure, end-tidal carbon dioxide, and heart rate were monitored continuously for 60 minutes and recorded. Serum osmolarity, sodium, potassium, chloride, arterial carbon dioxide pressure, arterial oxygen pressure, hemoglobin, lactic acid, and pH were measured immediately before infusion (zero time) and 20 and 60 minutes after infusion. Mean arterial pressure, cerebral perfusion pressure (CPP), mean flow velocity (MFV), and pulsatility index (PI) were also recorded and analyzed.

RESULTS

Intracranial pressure fell immediately after initiation of infusion with further significant decreases observed at 20 and 60 minutes (30.4 +/- 8.5, 24.3 +/- 7.4, and 23.8 +/- 8.3 mm Hg, respectively; P < .01). At these respective times CPP increased significantly (78.7 +/- 8.7, 83.2 +/- 7.8, and 87.2 +/- 12.8 mm Hg), PI dropped rapidly (1.51 +/- 0.42, 1.38 +/- 0.32, and 1.34 +/- 0.33) and MFV increased (66.26 +/- 25.91, 71.92 +/- 28.13, and 68.74 +/- 28.44). Serum sodium increased from 141.3 +/- 7.2 to 146.3 +/- 7.2 mmol/L after 20 minutes and returned to 144.3 +/- 7.36 mmol/L at 60 minutes. Potassium concentrations decreased significantly from 3.9 +/- 0.39 to 3.55 +/- 0.35 mmol/L after 20 minutes (P < .01). Lactic acid values at 0, 20, and 60 minutes were 1.6 +/- 0.5, 1.47 +/- 0.48, and 1.38 +/- 0.53 mmol/L, respectively (P < .01).

CONCLUSION

Rapid infusion of single dose daily of HS is a safe alternative for the treatment of elevated ICP in severe head injury. Further evaluations of long-term consequences and complications and of maximal tolerance to this treatment are required.

Treatment of cerebral edema

BACKGROUND

Cerebral edema is a potentially devastating complication of various acute neurologic disorders. Its successful treatment may save lives and preserve neurologic function.

REVIEW SUMMARY

Different pathophysiological mechanisms are responsible for the formation of cytotoxic and vasogenic edema. Yet, these 2 types of edema often coexist and their treatment tends to overlap, with the exception of corticosteroids, which should be only used to ameliorate vasogenic edema. Currently available to control brain swelling include osmotic agents (with emphasis on mannitol and hypertonic saline solutions), corticosteroids, hyperventilation, sedation (propofol, barbiturates), neuromuscular paralysis, hypothermia, and surgical interventions. This article discusses the indications, advantages, and limitations of each treatment modality following an evidence-based approach.

CONCLUSIONS

The therapy for brain edema remains largely empirical. More research aimed at enhancing our understanding of the pathophysiology of cerebral edema is needed to identify new and more effective forms of treatment.

Plasma arginine-vasopressin following experimental stroke: effect of osmotherapy

Neurohumoral responses have been implicated in the pathogenesis of ischemia-evoked cerebral edema. In a well-characterized animal model of ischemic stroke, the present study was undertaken to 1) study the profile of plasma arginine-vasopressin (AVP), and 2) determine whether osmotherapy with mannitol and various concentrations of hypertonic saline (HS) solutions influence plasma AVP levels. Halothane-anesthetized adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion with the intraluminal filament technique. Plasma AVP levels (means +/- SD) were significantly elevated at 24 h (42 +/- 21 pg/ml), 48 h (50 +/- 28 pg/ml), and 72 h (110 +/- 47 pg/ml), and returned to baseline at 96 h (22 +/- 15 pg/ml) following middle cerebral artery occlusion compared with sham-operated controls (14 +/- 7 pg/ml). Plasma AVP levels at 72 h were significantly attenuated with 7.5% HS (37 +/- 8 pg/ml; 360 +/- 11 osmol/l) compared with 0.9% saline (73 +/- 6; 292 +/- 6 osmol/l), 3% HS (66 +/- 8 pg/ml; 303 +/- 12 osmol/l), or mannitol (74 +/- 9 pg/ml; 313 +/- 14 osmol/l) treatment. HS (7.5%) significantly attenuated water content in the ipsilateral and contralateral hemispheres compared with surgical shams, 0.9% saline, 3% HS, and mannitol treatments. Peak plasma AVP levels were not associated with direct histopathological injury to the anterior hypothalamus. Attenuation of brain water content with 7.5% HS treatment coincides with attenuated serum AVP levels, and we speculate that this may represent one additional mechanism by which osmotherapy attenuates edema associated with ischemic stroke.

Treatment of massive cerebral infarction

Stroke is the third leading cause of death in the United States, with a person dying every 3 minutes of a stroke. Massive ischemic stroke accounts for 10% to 20% of ischemic strokes, has traditionally been associated with a high mortality and morbidity, and requires a unique management strategy. Recent advances in management, fueled by an increased understanding of the pathophysiology, may help decrease mortality and improve outcomes. Rapid access to reperfusion therapies remains the most critical element of stroke care and the cornerstone of therapy. This article focuses on newer therapies, including osmotic therapy, hypothermia, maintained normothermia, strict glycemic control, induced hypertension, and hemicraniectomy, all of which show promise for reducing mortality and improving functional outcome. These interventions have become integrated into neurologic intensive care units around the world. They are complicated, require a high level of expertise, and carry a significant learning curve. In order for these new management techniques to be effective, an expedited, aggressive, meticulous, and potentially prolonged medical management approach is needed. To accomplish this there is a growing need for focused specialists in the areas of neurointensive care and stroke.

Decompressive craniectomy as a therapeutic option in the treatment of hemispheric stroke

Even though severe hemispheric stroke represents a small subtype of ischemic stroke, the extreme morbidity and mortality necessitate aggressive management strategies to improve outcome. Decompressive craniectomy is an important therapeutic tool with demonstrated effects in significantly reducing intracranial hypertension and mortality from herniation related to cerebral edema and elevated intracranial pressure. Its effect on functional outcome and quality of life varies, but there is evidence to suggest beneficial effects in younger patients and in patients treated earlier. Although more prospective data are required to further identify specific indications for the procedure, it represents an important tool in treatment of nondominant hemispheric stroke.